Inflatable bag to absorb volume changes in gases within a sealed vessel

ABSTRACT

The interior of a pressure vessel shell containing an inert gas to prevent metal contamination during periods of shipment and/or storage is provided with an inflatable container adapted to accommodate volumetric changes in the protective inert gas caused by variations in atmospheric conditions. The arrangement permits the use of inert gas maintained substantially at atmospheric pressure throughout the entire protective period.

United States Patent [191 Stephenson Sept. 2, 1975 [54] INFLATABLE BAG TO ABSORB VOLUME 3,288,168 11/1966 Mercier et al 220/85 B CHANGES IN GASES .WITHIN A SEALED 3,348,728 10/1967 Love 220/63 R VESSEL 3,590,888 7/1971 Coleman. 220/63 R 3,747,800 7/1973 Viland 220/85 B [75] Inventor; Eben Albert Stephenson, Ite ah, 3,802,464 4/1974 Frank et a1. 138/30 1 FOREIGN PATENTS OR APPLICATIONS Assigneer Combustion Engineering, 1110-, 1,180,896 2/1970 United Kingdom 220/63 R Windsor, Conn.

[22] FiledZ Con 27, 1972 Primary Examiner-William T. Dixson, Jr.

Assistant Examiner-Joseph Man-Fu Moy PP N05 301,559 Attorney, Agent, or Firm-Frederick A. Goettel, Jr.

[52] US. Cl. 220/85 B; 220/22 [57] ABSTRACT [51] 5: i The interior of a pressure vessel shell containing an [58] held of z g g 86 85 inert gas to prevent metal contamination during peri- O/ 8 M: ods of shipment and/or storage is provided with an inflatable container adapted to accommodate volumetric changes in the protective inert gas caused by varia- [56] References cued tions in atmospheric conditions. The arrangement per- UNITED STATES PATENTS mits the use of inert gas maintained substantially at at- 2,014,264 9/1935 Patrick 220/ R mospheric pressure throughout the entire protective 2,387,598 10/1945 Mercier 220/63 R eri d. 2,758,747 8/1956 Stevens.... 220/63 R 2,764,950 10/1956 Finnell 206/D1G. 30 4 Clams, 2 Drawmg Flgllres INFLATABLE BAG TO ABSORB VOLUME CHANGES IN GASES WITHIN A SEALED VESSEL BACKGROUND OF THE INVENTION In many pressure vessel applications, such as for example, vessels utilized in performing certain chemical processes it is necessary to insure that the interior surface of the vessel be maintained free from corrosive attack. Such surfaces are highly susceptible to oxidation attack during periods of storage and/or shipment due to contact with moisture entrained in the atmosphere. It has been the practice to protect the interior surfaces of vessel shells during there periods by maintaining an inert atmosphere therewithin. This is normally accomplished by attaching temporary detachable seals to the shell openings and supplying an inert gas such as nitro gen to fill the shell interior.

In order to avoid the significant expense of installing, and thereafter removing welded seals to prevent leakage of the protective gas that might be caused by changes in gas volume due to variations in atmospheric conditions. it has been the practice to close the shell openings by inexpensive, readily detachable closures and to provide a source of pressurized inertgas to replace the gas lost due to the enevitable leakage that will occur through the closures. This arrangement is, itself, undesirable due to the fact that a source of inert gas, commonly a battery of pressurized nitogren gas bottles, must constantly be available to the shell both while it is being stored as well as while it is in transit to the plant site. There must also be provided connections and supply lines to connect the gas source to the shell interior as well as regulating apparatus to insure that the shell always contains the prescribed amount of protective gas. Since the pressure of the inert gas within the shell in these arrangements is above atmospheric more expensive closures and seals must be provided than would SUMMARY OF THE INVENTION According to the present invention means are provided in the described pressure vessel arrangement to enable protective inert gas to be utilized at substantially atmospheric pressure thereby to avoid the above mentioned problems and without the need for expensive welded seals. Vessel shells whose openings are closed by inexpensive, readily detachable closures are provided each within their interior with an inflatable container. The container is adapted to communicate with the atmosphere such that any changes in the specific volume in the inert gas caused by variations in ambient temperature or barometric pressure are accommodated by complementary changes in the volume of the container. The result is that no appreciable change occurs in the fluid pressure of the contained inert. gas. Therefore, where the gas pressure within the vessel is about atmospheric to pressure differential exists across the closure seals such that inert gas leakage outwardly of the shell or moisture-laden air leakage inwardly of the shell are both prevented.

For a better understanding of-the invention, its operating advantages and the specific objects obtained by its use, reference should be made to the accompanying drawings and description which relate to various embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevational view, partially in section of a vessel shell mounted for shipment and incorporating the present invention, and

FIG. 2 is an end view of the apparatus of FIG. 1.

DESCRIPTION OF Til-IE PREFERRED EMBODIMENT Referring to the drawing there is illustrated a generally cylindrical shell 10 defining a pressure vessel. The shell 10 is shown mounted for storage or shipment in a horizonal attitude upon a transport skid 12. The shell 10 is supported on the skid 12 upon longitudinally spaced mounting saddles l4 and secured thereon by means of tie cables 16 that surround the shell and whose ends are fastened to the mounting saddles on opposite sides of the skid.

One end of the shell 10 is closed by an integrally formed, generally spherical closure head 18. Its other end possesses an annular flange 20 that defines a shell opening 22. The flange 20 is provided with a plurality of circumferentially spaced threaded stud holes 24 whose principle function is to receive stud fasteners for attaching a closure head (not shown) to the shell opening 22 at final assembly of the pressure vessel. About its periphery the shell 10 is provided with a plurality of spaced radially extending nozzles 26 that penetrate the shell wall and establish points of connection between the interior of the shell and ancillary equipment that may be employed in the process for which the vessel is intended.

During periods of storage and/or shipment the shell opening 22 and the openings defined by the nozzles 26 are closed to isolate the shell interior from the external atmosphere. The opening 22 is closed by an enlarged circular plate 28 having a plurality of circumferentially spaced holes for the reception of studs 30 that are adapted to be secured to the stud holes 22 in the shell flange 20. An annular stiffener 32 formed of arcuate angle members is disposed externally of plate 28 and serves as an external bearing member for nuts that attach the studs 30. An annular bearing gasket 34 formed of soft rubber, or the like, is interposed between the plate 28 and flange 20 to seal the interface therebetween.

The ends of the respective nozzles 26 are closed by smaller closure plates 36 having a plurality of circumferentially spaced holes for reception of mounting studs 38 which, in the described arrangement, are weldedly attached about the circumference of friction bands 40. The friction bands 40 are arcuate members disposed in an opposed relation so as to surround the nozzles 26 and are secured in place by appropriate fasteners. Sealing gaskets 42, similar to the gasket 34 are disposed between the plates 36 and the outwardly facing surfaces on the nozzles 26 to seal the interfaces therebetwee n.

One of the nozzles 26 shown in FIG. 2 has its closure plate, indicated as 36a, provided with a connector fitting 44 that is adapted to receive a tubular line that connects the shell interior with a source (not shown) of inert gas, such as nitrogen or the like. Another nozzle 26 has its closure plate, indicated as 36b, provided with a fitting 46 that is adapted to receive a threaded plug and which serves as a vent for the shell interior. Means (not shown) are also provided, as hereinafter described, for introducing the protective inert gas to the shell interior in the prescribed manner.

According to the invention the interior of the shell 10 is provided with an inflatable container 48 formed of relatively thin plastic or rubber material. The container 48 should have a volume greater than that required to contain an amount of air received from the exterior of the shell in response to the contraction of the inert gas within the shell interior at the lowest expected temperature encountered by the shell during the protective period. Assuming the shell 10 has a contained volume of 1000 cubic feet and it may expect to experience a range of temperatures during the protective period from F to l20F the container must have a minimum capacity, as computed according to the General Gas Law,

of 260 cubic feet. The container 48 should have sufficient reserve capacity to maintain the pressure of the protective gas of the shell interior at about atmospheric pressure during the lowest temperature expected to be encountered.

The container 48 is connected to a closure plate, indicated as 36c, attached to a third nozzle 26 by means of an elongated pipe 50 that extends between a fitting 52 attached to the container and another fitting 54 secured to the closure plate 36c. The fitting 54 should be internally threaded to receive a plug for reasons hereinafter stated. As shown in FIG. 1, the pipe 50 can be provided with a union connector 56 to facilitate assembly and disassembly of the container 48 within the shell interior. The fitting 54 in the closure plate 36 is nor mally maintained open to the atmosphere and operates to place the interior of the container 48 in fluid communication with the atmosphere.

The operation of the hereindescribed organization is as follows. The shell with the inflatable container 48 installed therein is mounted upon the skid 12. The closure plates 28 and 36 with their associated sealing gaskets 34 and 42 are connected to the shell opening 22 and to the nozzles 26 to isolate the interior of the shell from the exterior atmosphere. The supply line 45 is attached to fitting 44 in closure plate 36a to place the shell interior in communication with a source of nitrogen or other inert gas. The fitting 54 in closure plate 360 is connected to a source of compressed air (not shown) to provide for the admission of air to the container 48 through pipe 50. At this time the plug associated with the vent fitting 46 in closure plate 36b is removed so that the shell interior is open to the atmosphere.

Metered air at ambient temperature is introduced at the fitting 54 from the compressed air source to partially inflate the container 48. The amount of air introduced must be sufficient to provide the container 48 with a volume equal to that representing the volume increase that will be under gone by the protective gas due to the maximum expected temperature rise to be cn countered during the protective period. Thereafter the line connecting the fitting 52 to the compressed air source is removed and the fitting 54 is plugged. At this point protective inert gas from a nitrogen source or the like is introduced to the shell interior through the supply line 45 that is connected to fitting 44. Admission of the gas is continued until air inside the shell 10 is sufficiently replaced by the dry inert gas to reach a predetermined dew point condition whereupon gas admission is terminated and the vessel permitted to return to atmospheric pressure. Fitting 46 in closure plate 36b is then closed by its associated plug. Lastly, the fitting 54 is unplugged thereby placing the interior of the container 48 in open communication with the external atmosphere. Such open communication continues during the entire protective period.

It is evident that, by means of the invention, the pressure of the inert gas contained within the sealed shell 10 will be maintained at about atmospheric pressure through the entire protective period regardless of variations in atmospheric conditions. As ambient temperature rises thus raising the temperature of the contained gas and increasing its specific volume, the expanded gas volume will operate to expel air from the container 48 through the pipe 50 and fitting 54. This reduces the portion of the shell interior occupied by the container thereby to maintain the pressure of the contained inert gas at about its original atmospheric pressure. Conversely, if ambient temperatures is reduced and the contained gas is caused to contract, the container 48 will inflate due to an influx of atmospheric air through the fitting 52 and pipe 50. This operates to increase the volume of the shell interior occupied by the container and conversely to reduce that portion occupied by the contained gas. The change is in an amount that will maintain the pressure of the contained inert gas at about atmospheric pressure.

Thus, because the fluid pressure of the contained protective gas within the shell interior is maintained substantially constant at about atmospheric pressure throughout the periods of shell storage and/or shipment the danger of gas leakage through the "closure plate seals is eliminated due to the fact that the pressure on both sides of the respective seals is equal. Since the possibility of gas leakage from the shell interior that might occur upon an increase in temperature of the contained gas is eliminated, the danger of entry of con taminating moisture laden air into the shell interior upon a cooling and contracting of the contained gas is avoided. These effects are achieved at a minimum cost resulting in a significant reduction in the overall expense involved in installing a pressure vessel of the described type.

It will be understood that various changes in the details, materials, and arrangements of parts which have been hereindescribed and illustrated in order to explain the nature of the invention, may be made by those skilled in the art within the principle and scope of the invention as expressed in the appended claims.

What is claimed is:

1. In combination with a vessel whose interior is substantially sealed from the external atmosphere and which contains a gaseous fluid, means for maintaining the fluid pressure of said gaseous fluid substantially constant during changes in atmospheric conditions comprising:

a. an inflatable container disposed within the interior of said vessel and having its interior in sealed relation therefrom; and

b. said container having an aperture operatively con necting the interior of said container in open communication with the atmosphere cxteriorly of said great as the maximum expected increase in volume of said gaseous fluid.

4. The combination recited in claim 1 wherein said inflatable container possesses a potential inflated volume that is greater than that required to contain the air received from the atmosphere in response to the greatest expected degree of contraction of said gaseous fluid. 

1. In combination with a vessel whose interior is substantially sealed from the external atmosphere and which contains a gaseous fluid, means for maintaining the fluid pressure of said gaseous fluid substantially constant during changes in atmospheric conditions comprising: a. an inflatable container disposed within the interior of said vessel and having its interior in sealed relation therefrom; and b. said container having an aperture operatively connecting the interior of said container in open communication with the atmosphere exteriorly of said vessel whereby expansions and contractions of the gaseous fluid contained within said sealed interior of said vessel are compensated by deflations and inflations respectively of said container.
 2. The combination recited in claim 1 wherein said inflatable container is partially inflated with air at atmospheric pressure.
 3. The combination recited in claim 2 wherein the volume of said partially inflated container is at least as great as the maximum expected increase in volume of said gaseous fluid.
 4. The combination recited in claim 1 wherein said inflatable container possesses a potential inflated volume that is greater than that required to contain the air received from the atmosphere in response to the greatest expected degree of contraction of said gaseous fluid. 